1. Field of the Invention
This invention relates to an apparatus of measuring the surface shape of a given sample.
2. Description of the Prior Art
For a compound semiconductor wafer which comprising a liquid phase epitaxial growth layer(s), for example, the surface state of the liquid phase epitaxial layer is itself one of the important product-specifications. Thus, the compound semiconductor wafer taken out from a production line is inspected for surface shape and acceptance or rejection is judged thereby.
A liquid phase epitaxial growth method is widely adopted for growing eptaxially a compound semiconductor layer(s) on a compound semiconductor substrate. In the compound semiconductor wafer comprising a liquid phase epitaxial growth layer(s), irregularities such as wrinkles, pits, and projections are liable to be formed in the surface portion of the liquid phase epitaxial growth layer.
In the fabrication of semiconductor devices such as light emitting diodes using the compound semiconductor wafer manufactured by the above-mentioned method, when the irregularities have large differences the in level, the electrodes formed in the regions containing such irregularities are rejective ones and consequently the semiconductor devices having such rejective electrodes are likewise rejective ones.
In the fabrication of various sorts of semiconductor devices from such compound semiconductor wafers comprising a liquid phase epitaxial growth layer(s), since the surface shapes of the liquid phase epitaxial growth layers influence the characteristics of the semiconductor devices as mentioned above, these surface shapes are needed to be examined to judge whether or not the surface shapes meet the standard of surface shape, namely the standard of surface irregularities, set in advance. And in the case of a wafer which is consequently found to contain a region(s) of a rejective surface shape, it is demanded that the position of this region is determined.
As method of measuring surface shapes, the moire fringe method which measures a surface shape by forming two regular distributions of light intensity on a given sample and overlapping these intensity distributions so as to form a moire fringe, the focussing method by vertically moving a given sample on which a beam of light is projected and measuring the shape in which the projecting beams of light are focussed, and the light interference method by using the phenomenon of light interference have been utilized.
The apparatuses to be used for these methods, however, call for complicate optical adjustments and necessitate time-consuming operations in order to measure surface shapes precisely and quantitatively. Further, the methods themselves impose conditions of their own on the measurable state of irregularities (degree of irregularities) of the surface of a given sample. Thus the conventional methods have been independently unable to implement measurement of the surface shapes of samples which have widely varied surface irregularities.
Also the method measuring a surface shape by projecting a collimated beam of light on a horizontally set sample, detecting the whole reflected light with a CCD, forming an image of the reflected light, displaying this image of the reflected light on a monitor, and visually examining the surface shape of the sample based on the image on the monitor has been adopted as well.
This method of measuring the surface shape of a sample by visually examining the image on the monitor allows a fully skilled operator to make a rough (qualitative) determination of the surface shape of the sample. It is, however, so deficient in accuracy as to measure quantitatively the surface shape of the sample.